In the past, water requiring treatment and purification for removal of iron and manganese was treated in a water treatment plant by adding oxygen to the water. This caused precipitation of impurities which were filtered out to leave purified water. Oxygen was typically added to the water in the form of pure oxygen, or by aeration of the water through the use of a cascade aerator. Because the concentration of oxygen necessary to precipitate metal ions from solution is comparatively low, metals iron and manganese were precipitated through the filtration process described above, wherein the filter encompassed one or more layers of sand through which the water was passed. Capital investment and operating costs for such a purification plant are high since the sand layers which function as the filter material must be regenerated from time to time to enhance the removal of the precipitated metal ions of manganese and iron.
Alternatively, ground water has been purified in situ as described in Swedish Patent Specification No. 6903544-2. Water containing oxygen or oxygen-releasing substances was introduced intermittently into an aquifer through a number of recharge wells or recharge pipes, arranged at a predetermined distance and surrounding a supply well or supply pipe. Oxygenated water introduced in this manner into an aquifer creates a suitable environment for the growth of certain microbes enhancing chemical and metabolic adsorption, oxidation and precipitation of compounds in the existing ground layers, thereby utilizing the ground layers as a reaction and filtration medium. The microbes employed are often sessile "37 gradient" organisms being active primarily in zones created between oxidizing and reducing conditions. Water containing oxygen or oxygen-releasing substances was added intermittently over a period of approximately twenty-four (24) hours. During the addition of oxygenated water or water containing oxygen-releasing substances, the supply well could not be used as a purified water source since concurrent use of the supply well and the recharge wells would cause the failure of the filtration mechanism or a disturbance in its operation, resulting in a deterioration of the quality of water. To supply water on a continuous basis, two or more supply wells or a suitable means for storage has been required to circumvent the above described disadvantages, enabling the withdrawal of purified water to be alternated between at least two supply wells or between the well and the storage means. Regeneration was performed on the dormant supply well or wells if necessary during withdrawal of purified water from the alternate supply source.
When water is withdrawn from a single supply well and conveyed to a recharge well or a plurality of recharge wells to allow concurrent use of the supply well, the flow pattern of recharged water becomes generally parallel to the flow pattern of the water to be purified. When this generally parallel flow pattern is established, a discontinuous radial purification pattern develops between the recharge wells and the supply well without being purified. This gradually reduces the operability of the supply well due to precipitation of iron and manganese which occurs in greatest measure in a smaller portion of the aquifer within close proximity to the supply well. This problem does not occur when using two or more supply wells as previously described, and by alternating the withdrawal of purified water between the supply wells thereby distributing the precipitation over a greater portion of the aquifer.